Recently, application of solar light is energetically investigated, which is infinity and generate no noxious substance. As the means practically used at the present time for utilizing the clean energy source of solar light, inorganic solar cells such as single crystal silicone for domestic use, polycrystal silicone, amorphous silicone, cadmium telluride and indium copper selenide are cited.
However, the solar cells, for example, the silicone type have drawbacks such as that extremely high purity is required so that complicated process including many steps is necessary and the production cost is raised.
On the other hand, many solar cells using an organic material are proposed. The organic solar cell includes a Schottky type photoelectric conversion element and a heterojunction type photoelectric conversion element in which a p-type organic semiconductor and an n-type organic semiconductor or a p-type organic semiconductor and an electron acceptable organic compound are joined. The organic semiconductor includes synthesized dyes or pigments such as chlorophyll and perylene, electroconductive polymers such as polyacetylene and composite materials of them. Such the materials are each made into a thin layer by a vacuum deposition method, a casting method or a dipping method for constituting the material of the cells. The organic materials have an advantage such that the cost is low and a large area material can be easily produced, but has a problem of low durability and the majority of them are low in the conversion efficiency as not more than 1%.
In such the situation, a solar cell showing suitable properties has been proposed by Dr. Gratzel in Switzerland, cf. Non-patent document 1 for example. The proposed cell is a dye sensitized type solar cell which is a wet type solar cell having a functional electrode composed of a porous titanium oxide thin layer spectrally sensitized by a ruthenium complex. Advantages of such the system are that the cell is cheep in the cost since a cheep oxide such as titanium oxide which is not necessary to highly purify and the range of applicable light widely covers visible range so as to effectively transducer solar light containing much visible light to electricity.
However, there is doubt as to supply of ruthenium when such the solar cells are practically used since ruthenium is limited resource. Moreover, ruthenium is high in the coast and has a problem of aging stability. Such the problems can be solved by exchanging ruthenium by a low-price and stable organic dye.
It has been known that a dye molecule having both of a π-electron conjugated system having electron donating ability and an acidic adsorption group gives a cell having high photoelectric conversion efficiency. Triarylamine derivatives are widely used as the electron donating π-electron conjugated system; cf. Patent Documents 1 to 4. However, the absorption peak of the solution of such the dye is not more than 500 nm and a problem that the absorption at the long wavelengths side is weak is left. A photoelectric conversion element capable of more effectively applying solar light can be obtained by expanding the absorption region of the dye to longer wavelength side. As a means for expanding the light absorption region to longer wavelength side, a means by formation of J-aggregate can be cited; cf. Patent Document 5, for example.                Patent Document 1: JP-A2005-123033        Patent Document 2: JP-A2006-079898        Patent Document 3: JP-A2006-134649        Patent Document 4: JP-A2006-156212        Patent Document 5: JP-A2005-019253        Non-patent Document 1: Nature, 353, 737 (1991), B. O. Regan, M. Gratzel        